Heat accumulator for vehicle

ABSTRACT

In a heat accumulator for a vehicle having a double tank structure comprised of an outer tank and an inner tank, which define therebetween an evacuated space, each of the outer and inner tanks has an opening. The opening of the outer tank and the opening of the inner tank are welded to each other over the entire peripheries thereof. A means for restricting vibration of the inner tank is provided in the accumulator. At least when the vehicle is stopped, the outer tank and the inner tank are not in contact with each other at any portion other than the welded portion.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat accumulator for a vehicle and, especially, to a heat accumulator for a vehicle in which the vibration resistance is improved.

[0003] 2. Description of the Related Art

[0004] In a conventional water-cooled-type internal combustion engine, a tank-type accumulator, in which cooling water is thermally isolated and stored, is generally provided in a cooling water circuit so that high-temperature cooling water which is discharged from the engine to warm up the engine, is introduced to the engine when the engine is re-started. The accumulator has a double tank structure comprised of an outer tank and an inner tank. The cooling water is efficiently thermally isolated in the inner tank by maintaining a vacuum in the space between the outer tank and the inner tank. For a more effective thermal isolation of the cooling water, it is preferable that a contact surface area of the outer tank 2 with the inner tank 3 of the accumulator 10 is as small as possible. In a conventional accumulator as shown in FIG. 1, the outer tank 2 is connected to the inner tank 3 only at the entire peripheral edges of respective openings of the tanks which are welded to each other as indicated at 6.

[0005] For example, the accumulator is mounted in a cantilever fashion to a side member of a vehicle through a bracket. Therefore, vibration produced during driving of the vehicle is transmitted to the accumulator, through the side member and the bracket, with relative ease. As a result, because the inner tank vibrates in the interior of the outer tank, tensile stress is repeatedly produced at the welded portion of the tanks, resulting in the possibility of breakage of the accumulator due to a fatigue fracture which may begin at the welded portion.

SUMMARY OF THE INVENTION

[0006] In order to solve the above-mentioned problem, the present invention is aimed at provision of an accumulator for a vehicle with high heat-isolation efficiency and improved vibration resistance.

[0007] According to a first embodiment of the present invention, a vehicle accumulator has a double tank structure comprised of an outer tank and an inner tank, which define therebetween an evacuated space. In the vehicle accumulator, each of the outer tank and the inner tank has an opening. The opening of the outer tank and the opening of the inner tank are welded to each other over the entire peripheries of the openings. A means for restricting vibration of the inner tank is provided on the inner tank or the outer tank. At least, when the vehicle is stopped, the outer tank and the inner tank are not in contact with each other at any portion other than the welded portion so as to prevent heat conduction. Because the outer tank and the inner tank are not in contact with each other at any portion other than the welded portion when the vehicle is stopped, the heat of cooling water stored in the inner tank is hardly transmitted to the outer tank and the vibration of the inner tank can be restricted while a vehicle is moving. That is, the vehicle accumulator can exhibit both high heat-isolation efficiency and high vibration resistance.

[0008] According to a vehicle accumulator of a second embodiment of the present invention, the vibration restricting means is a stopper which is provided on an inner surface of the outer tank or on an outer surface of the inner tank, so as to limit the amplitude of vibration of the inner tank to a small value. Thus, because the outer tank and the inner tank, one of which is provided with the stopper, are not in contact with each other at any portion other than the welded portion when the vehicle is stopped, the heat of the cooling water stored in the inner tank is hardly transmitted to the stopper and the outer tank, and the vibration of the inner tank can be restricted by the stopper while the vehicle is moving.

[0009] According to a vehicle accumulator of a third embodiment of the present invention, the vibration restricting means is a dynamic damper which is mounted on the inner tank. Thus, because the outer tank and the inner tank which, is provided with the dynamic damper, are not in contact with each other at any portion other than the welded portion all the time, the heat of the cooling water stored in the inner tank is hardly transmitted to the outer tank and the vibration of the inner tank can be restricted by the dynamic damper when the vehicle is moving.

[0010] According to a vehicle accumulator of a fourth embodiment of the present invention, the vibration restricting means is comprised of a first magnet attached to the inner surface of the outer tank and a second magnet attached to the outer surface of the inner tank. The same poles of the first and second magnets are opposed to each other, so that the amplitude of vibration of the inner tank can be restricted due to magnetic repulsion. Thus, because the outer tank provided with the first magnet and the inner tank provided with the second magnet are not in contact with each other at any portion other than the welded portion all the time, the heat of the cooling water stored in the inner tank is hardly transmitted to the outer tank, and the vibration of the inner tank can be restricted by the first and second magnets while the vehicle is moving.

[0011] According to a vehicle accumulator of a fifth embodiment of the present invention, the vibration restricting means is a lock mechanism comprised of a first engagement portion provided on the outer tank and a second engagement portion provided on the inner tank. The second engagement portion can be selectively engaged with and disengaged from the first engagement portion. The first engagement portion engages with the second engagement portion so that the outer tank and the inner tank are mechanically connected to each other through the lock mechanism. Thus, the outer tank and the inner tank are not in contact with each other at any portion other than the welded portion when the vehicle is stopped, so that the heat of the cooling water stored in the inner tank is hardly transmitted to the stopper and the outer tank, and the vibration of the inner tank can be restricted while the vehicle is moving.

[0012] According to a vehicle accumulator of a sixth embodiment of the present invention, at least one of the first engagement portion and the second engagement portion can be driven by a signal. The lock mechanism is mechanically locked by the engagement of the first engagement portion and the second engagement portion, at least one of which is driven.

[0013] According to a vehicle accumulator of a seventh embodiment of the present invention, the signal is comprised of a signal issued in accordance with a moving state of the vehicle.

[0014] According to a vehicle accumulator of a eighth embodiment of the present invention, the first engagement portion is extendably and retractably driven so as to be engaged by the second engagement portion and the signal is comprised of a signal issued during movement of the vehicle.

[0015] According to a vehicle accumulator of a ninth embodiment of the present invention, the stopper is provided on the inner peripheral surface of the outer tank or the outer peripheral surface of the inner tank, and is comprised of members having parts which are opposed to each other in the radial direction of the inner tank.

[0016] According to a vehicle accumulator of a tenth embodiment of the present invention, the stopper is comprised of a cylindrical member provided on the entire inner periphery of the outer tank or the entire outer periphery of the inner tank.

[0017] The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In the drawings:

[0019]FIG. 1 is a sectional view of a conventional vehicle accumulator.

[0020]FIG. 2 is a sectional view of a vehicle accumulator according to Embodiment 1 of the present invention.

[0021]FIG. 3 is a graph showing a stress of the welded portion with respect to a vibration frequency when the vehicle accumulator of Embodiment 1 is used.

[0022]FIG. 4 is a sectional view of a vehicle accumulator according to Embodiment 2 of the present invention.

[0023]FIG. 5 is a graph showing a stress of the welded portion with respect to a vibration frequency when the vehicle accumulator of Embodiment 2 is used.

[0024]FIG. 6 is a sectional view of a vehicle accumulator according to Embodiment 3 of the present invention.

[0025]FIG. 7 is a graph showing a stress of the welded portion with respect to a vibration frequency when the vehicle accumulator of Embodiment 3 is used.

[0026]FIG. 8 is a sectional view of a vehicle accumulator in an operative position according to Embodiment 4 of the present invention.

[0027]FIG. 9 is a sectional view of a vehicle accumulator in an inoperative position according to Embodiment 4 of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0028] Embodiments of the present invention will be explained below with reference to attached drawings. First, Embodiment 1 of the present invention will be explained. FIG. 2 is a sectional view of a vehicle accumulator according to Embodiment 1 of the present invention. Numeral 10 designates the entire vehicle accumulator. The accumulator 10 has a double tank structure comprised of an outer tank 2 and an inner tank 3. Each of the outer tank 2 and the inner tank 3 has an opening at its bottom surface. The openings of the tanks 2 and 3 are connected to each other over their entire peripheries, for example, by welding, to form a welded portion 6. The outer tank 2 and the inner tank 3 are not in contact with each other at any portion other than the welded portion 6 and the space between the outer tank 2 and the inner tank 3 is evacuated so that it is ensured that the heat of the cooling water stored in the inner tank is hardly transmitted to the outer tank.

[0029] Next, a valve (plug) 4 which is provided on the inner tank 3 will be explained. The valve 4 is pressed and brought into contact with an interior of a welded portion 6 of an accumulator 10 in order to seal the opening of the inner tank 3, so that the entire periphery of the welded portion 6 and the inner tank 3 are sealed. Further, an O-ring 7 is inserted in the gap between the inner tank 3 and the valve 4, i.e., in the portion above the sealed portion, in order for the opening of the inner tank 3 to be more effectively sealed. The valve 4 has a hole through which an inlet pipe 8 extends and a hole through which an outlet pipe 9 extends, so as to admit the cooling water to flow into and out of the inner tank 3 through the valve 4. Each of the inlet pipe 8 and the outlet pipe 9 is a part of the cooling water circuit of the internal combustion engine.

[0030] A method of mounting the accumulator 10 will now be explained. A bracket 5 is used to mount the accumulator 10 on the vehicle body. One end 5 a of the bracket 5 surrounds the entire peripheral edge of the outer tank 2 to hold the accumulator 10, and the other end 5 b of the bracket 5 is attached to a side member 1 of the vehicle body. As shown in FIG. 2, the accumulator 10 is mounted, in a cantilevered fashion, to the vehicle body through two brackets 5, according to the present embodiment.

[0031] Next, the operation of the accumulator 10 when vibrating will be explained. When driving the vehicle, each part of the vehicle is subject to vibration mainly because the tires move upward and downward due to projections and depressions on the road. Especially, at the vehicle accumulator, the vibration is transmitted through the side member 1 and the bracket 5. In this case, the outer tank 2 and the inner tank 3 of the accumulator 10 are welded to each other only at the welded portion 6 as above described and, hence, the vibration rigidity is low. Thus, the inner tank 3 vibrates in the interior of the outer tank 2 and tensile stress is repeatedly produced at the welded portion 6 of the outer tank 2 and the inner tank 3. Because the magnitude of the tensile stress is beyond the fatigue limit which can cause the fatigue fracture, there is a possibility that the accumulator 10 may be broken due to a fatigue fracture which may occur when the number of the repeated occurrences of tensile stress reaches a predetermined number. This results in the lack of vibration resistance of the accumulator 10.

[0032] Regarding the above problem, according to the present invention, while the requirement that the outer tank 2 is spaced from the inner tank 3, when the vehicle is stopped and in order to increase the thermal isolation efficiency, is satisfied, the vibration of the outer tank 2 and the inner tank 3 is restricted by using vibration restricting means described below. Therefore, the tensile stress produced at the welded portion 6 is always reduced to within the fatigue limit, so that no fatigue fracture occurs in the accumulator 10, that is, the vibration resistance can be improved.

[0033] In Embodiment 1, as the vibration restricting means, cylindrical stoppers 11 a and 11 b are located on a part or the entirety of the inner periphery of the outer tank 2 or on a part or the entirety of the outer periphery of the inner tank 3. That is, the stopper 11 a or 11 b surrounds the inner tank 3 in the radial and outward direction of the inner tank 3. If the stoppers 11 a and 11 b are provided on a part of the inner periphery or the outer periphery of the outer tank 2 or the inner tank 3, the stoppers 11 a and 11 b are comprised of a plurality of stopper elements opposed to each other in the radial direction of the inner tank 3. Therefore, the amplitude of vibration of the inner tank 3 is restricted by the stopper 11 a or 11 b.

[0034] The restriction of the vibration and the reduction of the stress will be explained with reference to FIG. 3. FIG. 3 is a graph showing a relationship between a frequency f of the vibration of the inner tank 3 and a tensile stress σ of the welded portion 6. If the vibration restricting means is not used, the stress σ is beyond the fatigue limit σ_(w) in a specific frequency area, as indicated by a stress curve A shown by a dotted line. However, a value of a stress curve B, shown by a solid line, of the present embodiment can be reduced to be smaller than the fatigue limit σ_(w) in an arbitrary frequency area because the vibration is reduced by the stopper 11 a or the stopper 11 b. That is, fatigue fracture can be prevented so that the vibration resistance of the accumulator can be improved.

[0035] Next, Embodiment 2 will be explained. FIG. 4 is a sectional view of the vehicle accumulator according to Embodiment 2. The second embodiment is almost the same as Embodiment 1 except that the dynamic damper 12 is provided to constitute the vibration restricting means in the second embodiment. The dynamic damper 12 is provided on the upper surface of the inner tank 3. The dynamic damper 12 is comprised of a weight 12 a and a spring 12 b inserted between the weight 12 a and the upper surface of the inner tank 3. As above constructed, the vibration of the inner tank 3 which vibrates in the interior of the outer tank 2 while driving the vehicle, can be reduced by the dynamic damper 12 mounted to the inner tank 3.

[0036] The restriction of the vibration and the reduction of the stress will be explained with reference to FIG. 5. FIG. 5 is a graph showing a relationship between the frequency f of the vibration produced at the welded portion and the tensile stress σ produced at the welded portion. While the stress curve A showing the stress when the vibration restricting means is not used is beyond the fatigue limit σ_(w), the value of the stress curve C, shown by the solid line, of the present embodiment can be reduced to be smaller than the fatigue limit σ_(w) in an arbitrary frequency area because the vibration is reduced by the dynamic damper 12, so that the vibration resistance of the accumulator can be improved.

[0037] Next, Embodiment 3 will be explained. FIG. 6 is a sectional view of the vehicle accumulator according to Embodiment 3. The third embodiment is almost the same as the above-mentioned embodiments except that a magnet 13 is provided to constitute the vibration restricting means in the third embodiment. The magnet 13 is comprised of a cylindrical first magnet 13 a attached to the inner surface of the outer tank and a cylindrical second magnet 13 b attached to the outer periphery of the inner tank. The first and second magnets 13 a and 13 b are opposed to each other at the same polarity. Consequently, the inner tank 3 provided with the second magnet part 13 b is biased toward the center in the outer tank 2 due to magnetic repulsion of the first magnet part 13 a, resulting in a restriction the vibration of the inner tank 3.

[0038] The restriction of the vibration and the reduction of the stress will be explained with reference to FIG. 7. FIG. 7 is a graph showing a relationship between the frequency f of the vibration produced at the welded portion and the tensile stress σ produce at the welded portion. The value of the stress curve D, shown by the solid line, of the present embodiment can be reduced to be smaller than the fatigue limit σ_(w) in an arbitrary frequency area because the vibration is reduced by the magnet 13, so that the vibration resistance of the accumulator can be improved.

[0039] Lastly, Embodiment 4 will be explained. FIG. 8 is a sectional view of the lock mechanism in an operative position in the vehicle accumulator according to Embodiment 4. FIG. 9 is a sectional view of the lock mechanism in an inoperative position in the vehicle accumulator according to Embodiment 4. The fourth embodiment is almost the same as the above-mentioned embodiments except that the lock mechanism 14 is provided to constitute the vibration restricting means in the fourth embodiment. As shown in FIGS. 8 and 9, the lock mechanism 14 is comprised of a base 14 b provided on its upper inner surface, an extendable and retractable shaft 14 a which is the first engagement portion and which is provided in the base 14 b, and a recess 14 c being the second engagement portion which can be engaged with the shaft 14 a and which is provided on the upper outer surface of the inner tank 3. The lock mechanism 14 is mechanically locked by the engagement of the first engagement portion and the second engagement portion. The base 14 b has therein a servomotor (not shown). The shaft 14 a connected to the servomotor is extended or retracted due to the rotation of the servomotor. The shaft 14 a is engaged, by the recess 14 c, in its extended position, so as to secure the outer tank 2 to the inner tank 3, and is retracted in the base 14 b in its retracted position. The servomotor is also connected to a vehicle speed sensor showing the moving state of the vehicle through an EPU (not shown) and can control the lock mechanism 14 so that the shaft 14 a is extended or retracted in accordance with an output signal from the vehicle speed sensor.

[0040] According the present embodiment, while the vehicle is driven, that is, when the velocity detected by the vehicle speed sensor is not zero, the shaft 14 a is extended to be engaged by the recess 14 c so as to secure the outer tank 2 to the inner tank 3 and, hence, fatigue fracture can be prevented because little vibration occurs. Also, when the vehicle is stopped, and the accumulator 10 is required to provide effective thermal isolation of the cooling water, that is, when the velocity detected by the vehicle speed sensor is zero, the contact surface area of the outer tank 2 with the inner tank 3 can be reduced by retracting the shaft 14 a, so that both the heat-isolation efficiency and the vibration resistance of the accumulator 10 can be improved.

[0041] In Embodiment 4, the lock mechanism is released, i.e., the shaft 14 a is retracted when the velocity of the vehicle is zero. However, in order to prevent the lock from being released when the vehicle is temporarily stopped due to a traffic light, etc., alternative unlocking conditions can be used, in which the lock mechanism is unlocked, for example, when the velocity of the vehicle being zero lasts for more than 30 minutes, or when an ignition key is off.

[0042] In a modified embodiment of the stopper 11 in Embodiment 1, the stopper which is provided on the entirety of the inner periphery of the outer tank or the outer periphery of the inner tank in Embodiment 1, may be provided on only a part of the periphery, in order to lighten the stopper 11. In this modification, by way of example, the stopper 11 a and the stopper 11 b are each divided into eight stopper elements which are spaced from each other at an angular distance of 45°, in the circumferential direction. In a modified embodiment of the magnet 13 in Embodiment 2, in order to lighten the magnet 13, the first magnet 13 a and the second magnet 13 b may be provided on only a part of the periphery. In this modification, by way of example, the first magnet 13 a and the second magnet 13 b are each divided into eight elements which are spaced from each other at an angular distance of 45°, in the circumferential direction.

[0043] While the invention has been described by reference to specific embodiments chosen for purposes of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention. 

1. A heat accumulator for a vehicle having a double tank structure comprised of an outer tank and an inner tank, which define therebetween an evacuated space, wherein each of the outer and inner tanks has an opening; the opening of the outer tank and the opening of the inner tank are welded to each other over the entire peripheries thereof; a means for restricting vibration of the inner tank is provided on the inner tank or the outer tank; and the outer tank and the inner tank are not in contact with each other at any portion other than the welded portion so as to prevent heat conduction, at least when the vehicle is stopped.
 2. A heat accumulator for a vehicle as set forth in claim 1, wherein said vibration restricting means comprises a stopper which is provided on the inner surface of the outer tank or on the outer surface of the inner tank so as to limit the amplitude of vibration of the inner tank to a small value.
 3. A heat accumulator for a vehicle as set forth in claim 1, wherein said vibration restricting means comprises a dynamic damper which is mounted to the inner tank.
 4. A heat accumulator for a vehicle as set forth in claim 1, where in said vibration restricting means comprises a first magnet provided on the inner surface of the outer tank and a second magnet provided on the outer surface of the inner tank, the first magnet and the second magnet having the same poles opposed to each other. so as to restrict the amplitude of vibration of the inner tank due to magnetic repulsion.
 5. A heat accumulator for a vehicle as set forth in claim 1, wherein said vibration restricting means comprises a lock mechanism comprised of a first engagement portion provided on the outer tank and a second engagement portion provided on the inner tank, said second engagement portion being selectively engageable with and disengageable from the first engagement portion, the outer tank and the inner tank being mechanically connected to each other through the lock mechanism, when the first engagement portion is engaged by the second engagement portion.
 6. A heat accumulator for a vehicle as set forth in claim 5, wherein at least one of the first and second engagement portions can be driven by a signal and the lock mechanism is mechanically locked by the engagement of the first engagement portion and the second engagement portion, at least one of which has been driven.
 7. A heat accumulator for a vehicle as set forth in claim 6, wherein said signal comprises a signal issued in accordance with a moving state of a vehicle.
 8. A heat accumulator for a vehicle as set forth in claim 7, wherein the first engagement portion can be extendably and retractably driven so as to be engaged by the second engagement portion and the signal is comprised of a signal issued during driving of the vehicle.
 9. A heat accumulator for a vehicle as set forth in claim 2, wherein said stopper is provided on the inner peripheral surface of the outer tank or on the outer peripheral surface of the inner tank and is comprised of members having parts which are opposed to each other in the radial direction of the inner tank.
 10. A heat accumulator for a vehicle as set forth in claim 9, wherein said stopper is comprised of cylindrical members which are provided on the entirety of the inner peripheral surface of the outer tank or the outer peripheral surface of the inner tank. 